Field of the Invention
The present invention relates to an exhaust gas recirculation apparatus for engine to allow a part of exhaust gas discharged from the engine to flow in an exhaust passage and recirculate back into the engine.
Related Art
The above type of technique is heretofore used in a vehicle engine, for example. An exhaust gas recirculation (EGR) apparatus is configured such that a part of exhaust gas discharged from a combustion chamber of an engine to an exhaust passage after combustion is introduced as EGR gas into an intake passage through an EGR passage, and then mixed with intake air flowing in the intake passage, and this mixture recirculates back into a combustion chamber. The EGR gas flowing in the EGR passage is regulated by an EGR valve provided in the EGR passage. This EGR can mainly reduce nitrogen oxide (NOx) in the exhaust gas and improve fuel consumption while the engine is subjected to partial load.
The exhaust gas from the engine contains no or little oxygen. Accordingly, when a part of exhaust gas is mixed with intake air by EGR, the concentration of oxygen in the intake air becomes lower. In the combustion chamber, therefore, a fuel burns in a low oxygen concentration state. This can decrease a peak temperature during combustion, thereby restraining the generation of NOx. In a gasoline engine, the EGR can prevent the oxygen content in the intake air from increasing and thus reduce a pumping loss of the engine even when a throttle valve is in to some extent closed state.
Herein, for further improvement of fuel consumption of an engine, it is recently conceived to perform EGR in every engine operating region. Thus, high EGR is demanded. To realize the high EGR, it is necessary to remodel a conventional apparatus by increasing an inner diameter of the EGR passage or increasing the size (diameter) of a valve element and the area of a flow path opening of a valve seat of an EGR valve.
Japanese patent application publication No. 2010-281303 (JP-A-2010-281303) discloses one example of a controller of an engine. This controller is provided with an EGR device and an intake pipe length switching mechanism. The EGR device includes an EGR passage and an EGR valve. The intake pipe length switching mechanism is provided in an intake passage and configured to selectively switch between a long passage and a short passage by means of a changeover valve. The EGR passage is connected to the intake passage at a position downstream of a throttle valve and upstream of the changeover valve. When an accelerator pedal of the engine is returned from a depressed state to a full-close position, the throttle valve is controlled to its closing side. At that time, when the EGR valve is closed from an open state, the changeover valve being in a long position to open the long passage is controlled to a short position to open the short passage. Alternatively, when the accelerator pedal is returned to the full-close position and thereby the throttle valve is closed, the EGR valve is controlled from the open state to a closing side and the changeover valve is controlled to the short position. This can improve EGR response property.